Apparatus automatically controlling the correlation between time and air pressure



Feb. 25, 1969 KAZUHIRO MORlYAMA ET AL 3,429,336

APPARATUS AUTOMATICALLY CONTROLLING THE CORRELATION BETWEEN TIME AND AIRPRESSURE Filed Dec. 7. 1966 ATTORNEYS United States Patent 11 ClaimsABSTRACT OF THE DISCLOSURE The pressure in a vessel is transformed intoan analogue signal which is applied to a comparison network to becompared with another signal varying according to a predeterminedprogram. The resulting difference signal controls throughelectromechanical control means a valve at the inlet of the vessel. Acorrection circuit coupled with said valve produces a compensationsignal which is fed back to said electromechanical means to insurecorrect controlling action of said valve.

The present invention relates generally to an apparatus forautomatically and simultaneously controlling the time and the pressurein a casting process, and it relates more particularly to an apparatusfor automatically controlling the pressure as a function of time in alow-pressure die casting process.

The present application is a continuation-in-part of our co-pendingapplication Ser. No. 325,823, filed Nov. 25, 1963 and now abandoned.

The present invention relates generally to an apparatus forautomatically controlling the pressure in a vessel. More particularly,the present invention relates to an apparatus for automaticallycontrolling according to a predetermined program a fluid pressure in avessel for a die casting process.

In low-pressure die casting processes, especially when the object beingcast has an excessively elongated form, and if the metal being used hasa large specific gravity, the pressure over the molten metal in themelting vessel becomes excessively reduced when the air in the mold issucked out through the upper part of the mold while the molten metal issucked into the mold. Therefore, it becomes necessary to supplyadditional pressure to the surface of the molten metal in the vessel.However, after completion of the solidification of the molten metal inthe mold, and before the molten metal would be allowed to solidify inthe feeding pipe, the additional pressure applied to the surface of themolten metal in the mold should be reduced back to the atmosphericpressure so that the molten metal which is in the feeding pipe couldreturn into the vessel. In low-pressure die casting processes,especially in the cases mentioned above, when the object being cast hasan excessively elongated form, it becomes very diflicult to control thespeed of rising and the speed of solidification of the molten metal.Therefore, the above described so-called suck-in and pressurize methodof casting has not been put into practice so far for the difficultiesencountered therein.

In a low-pressure die casting system it may be required that the initialpressure be applied to the surface of the metal in the vessel and thenbe raised slowly by approximately 0.4 kilogram per square centimeterwithin a specified time interval, which may be a period of time between20 and 120 seconds. The pressure may be kept ice at a second value ofbetween 0.7 and 1.0 kg./cm. for a second time interval. Since the twotime intervals and the fixed pressure values must "be controllable,means must be provided to set the diflerent values of pressure and thetime intervals according to the desired operation.

Formerly such operations were performed by manually controlling theopening of the pressure feeding valve. In such an operation, it is verydiificult to control the pressure at the desired value; and there areother deficiencies in this former operation such as that the quality ofthe castings is not uniform because the pressure tends to be forced in ashort time, and the operation cannot be repeated with the same degree ofaccuracy over a number of casting cycles.

It is, therefore, an object of the present invention to provide animproved apparatus for automatically controlling the pressure as afunction of time in a lowpressure die casting process.

It is another object of the invention to provide an apparatus by whichthe pressure over the molten metal is controlled in accordance with apredetermined program, and by which any deviations from the pressure setby the predetermined program are instantaneously corrected.

It is still another object of the present invention to pro vide aprogramming means for an apparatus controlling the pressure inaccordance with a predetermined program in a low-pressure die castingprocess, in which the desired pressure conditions are attained by simpleand reliable mechanical means.

It is still a further object of the present invention to provide in anapparatus controlling the pressure conditions in a low-pressure diecasting system a programming means of simple mechanical nature which iscorrelated With a timing apparatus and which produces a reference signalrepresenting the desired pressures as a function of time.

In accordance with the invention, in a control apparatus for controllingthe gas pressure in a vessel, a pneumatic circuit is provided whichconnects the vessel to a pneumatic source, pressure sensing means on thevessel for producin g a signal in response to the instantaneous pressureexisting in the vessel, and a programming means which produces an outputsignal representative of a predetermined pressure as a function of time,and also control means which respond both to the output of the pressuresensing means and to the output of the programming means and are adaptedto compare the aforesaid outputs to provide a balance signal in responseto a diflerence between the aforesaid outputs and to effect theinstantaneous position of a valve means disposed in the aforementionedpneumatic circuit and regulate the valve means either to permit the flowof pressurized fluid to the vessel or to restrict the flow ofpressurized fluid as flowing to the vessel in dependence of the sign ofthe balance signal.

The invention also provides in the pressure control apparatus that theprogramming means includes a rotatably mounted disc with which a timingelement is coupled so that rotation of the disc, as controlled by thetiming element, produces an output signal which represents apressure-time signal which is used as a reference signal to compare samewith an output signal from the pressure sensing means.

In accordance with the invention the aforementioned programming disc ismounted for rotation on a fixed axis and the outer edges of the disc areplaced at different distances from the center thereof, so that the edgeportions of the disc sweep a varying area with respect to the center ofthe disc. That is, if the edge portions of the program disc are tracedby a lever, which is pivotally mounted at a fixed point and the free endof which is adapted to ride on the edge portion of the program disc, thefree end of the pivotable lever will sweep an area which if projected ona time axis corresponding to the time required by the disc to completeone revolution will be bounded by curve representing a time-pressurefunction. The shape of the disc is made in accordance with the desiredtime-pressure curve, The disc is interchangeable to enable theattainment of any desired time-pressure curve by the control apparatusin accordance with the invention.

In accordance with the invention, the lever is coupled with its free endin tracing relationship with the edge portions of the disc and hasconnected thereto and to move therewith a wiper arm of a potentiometer,which potentiometer develops an electrical signal representative of thepredetermined pressure desired in the particular operation. The pressuresensing means connected to the vessel provide a signal representative ofthe instantaneou pressure above the molten metal and such signal. is fedto drive a servo-motor which in turn operates the wiper arm of anotherpotentiometer and develops a signal thereon representative of theinstantaneous pressure in the vessel. The first mentioned and the lastmentioned otentiometers are arranged in a bridge circuit, that is, avoltage appearing at their respective wiper arms is compared and fedinto subsequent circuits adapted to respond to a balance between suchvoltages on the wiper arms, so that a servomotor is actuated by thebalance in the direction depending upon the sign of such balance, tooperate a valve set in a pneumatic circuit connecting the vessel to apneumatic source and causing the pneumatic circuit to be restricted oropened in accordance with the signal fed to the servo-motor operatingthe valve.

The invention will become more readily apparent from the followingdescription of a specific embodiment thereof shown, by way of example,and illustrated in the accompanying drawings, in which:

FIG. 1 is a diagrammatic showing of the principles of operation of thecontrol apparatus of the present invention;

FIG. 2 is a circuit diagram showing the circuit for developing areference signal by the programming means and its comparison with theinstantaneous signal developed by the pressure sensing means and theirconduction to the valve controlling servo-motor;

FIG. 3 is a circuit diagram showing a bridge circuit for developing asignal in response to the pressure sensing means;

FIG. 4 is a circuit diagram showing the connection of the programmingmeans and the respective valve means;

FIG. 5 is a diagrammatic showing of the disc of the programming meanswith its associated tracing lever in several operating positions; and

FIG. 6 is a pressure-time diagram representing the reference pressure astraced out by the lever engaging the program disc.

With reference to the drawings, particularly to FIG. 1, it is seen thatthe pressure vessel 1 containing a molten metal has a pneumatic circuitarranged therearound, in which the branch of the circuit designated bythe reference character P connects the vessel to a source of pneumaticpressure (not shown), whereas the branch of the pneumatic circuitdesignated by P connects the vessel 1 through a valve V to theatmosphere in a manner hereinafter described. The pneumatic circuitbranch P contains a valve V which has only a fully opened and a fullyclosed position and is operated by a solenoid upon certain conditions inthe operating stage of the control apparatus as hereinafter described.The circuit branch P contains a servo-motor operated valve MV which isactuated by appropriate manner hereinafter described by the controllingmeans shown as block C in FIG. 1 in response to a correcting signaldeveloped by the controlling means C as need may arise to permit orrestrict the flow of pressurized fluid in circuit branch P to the vessel1 in accordance with the type of pressure conditions existing in vesselI sensed by pressure sensing means P which is operatively connected tothe controlling means C for comparing the instantaneous pressure sensedby it, An indicator 10 is placed in cooperation with the controllingmeans C to indicate the instantaneous pressure in the vessel and whichalso actuates a switch S for purposes hereinafter described. Anotherindicator I may be placed upstream of the motor valve MV to indicate thepressure supplied by the pressure source (not shown).

Referring now to FIG. 2, it is seen that the vessel 1 containing themolten metal which is to be raised into a die (not shown) by supplyingpressurized fluid to the vessel from a source of pneumatic pressurethrough pneumatic circuits as shown in FIG. 1, has a. pressure sensingdevice connected thereto which includes a pressure sensing tube P whichis preferably of the Bourdon-type tube well known in the art and whichis adapted to produce mechanical movements as its output in response tothe pressure variations within the vessel. The mechanical movementsproduced by the Bourdon tube are translated into electrical signals bymeans of a transducer 19, such as a differential transformer having amovable core responsive to the mechanical movements produced by theBourdon tube and which transformer produces an output representative ofthe pressure variations within the vessel. Other transducers than adifferential transformer are possible, such as a piezo-electrictransducer, the output of which would be also representative of thepressure variations in vessel 1. The output of the differentialtransducer 19, or of a similar transducer, is fed into a servomotor (notshown) the rotation of which operates a linkage 11 which is connected toa wiper arm B of a balanced bridge circuit 20. The balanced bridgecircuit 20 being shown in more detail in FIG. 3 includes a pair ofresistance branches 21, 22 connected across a voltage source V into abalanced bridge circuit. Resistor 22 has the wiper arm B slidablyassociated therewith which, as aforementioned, is operated by linkage 11in response to the output of the transducer 19 through the servomotor.The resistor 21 has a wiper arm A slidably associated therewith andwhich is operable by a servo-motor 24 at the output of the bridgecircuit 20 to balance bridge circuit 20 in a known manner. As moreclearly seen in FIG. 3, when wiper arm B is moved in the direction of Ior II in dependence of decreasing or increasing pressures in the vessel1, then the bridge becomes unbalanced and, such unbalance in dependenceof the direction of movement of wiper arm B may have a sign of or andhave a magnitude e which is fed into amplifier 23 to the output of whichthe servo-motor 24 is connected. The servo-motor in accordance with thesign of the output e rotates in a direction corresponding to such sign,and with a feedback arm 25 operates wiper arm A sliding on resistor 21to balance the bridge in a known manner by moving wiper arm A in thedirection of III or IV depending of the direction of movement of thewiper arm B. The servo-motor 24 represents with the direction and timeof its rotation the output e of the balanced bridge circuit 20 (which asaforesaid is representative of the pressure variations in vessel 1), andis connected to operate a wiper arm 31 of a control means preferablycomprising a bridge circuit 30. The wiper arm 31 of the bridge circuit30 is adapted to slide on a resistor 33 and in response to the movementimparted thereto by the servomotor 24 develops a voltage 2 which isrepresentative of the instantaneous pressure within vessel 1, and whichvoltage is compared with another voltage representing the desiredpressure conditions in the vessel as hereinafter described.

As pointed out above, it is desired that the pressure within the vessel1 over the molten metal body should be maintained at differentmagnitudes during different time intervals according to the type ofcasting to be made and the material used in the casting processv Inorder to attain and maintain the required pressure magnitudes, aprogramming device is provided which produces a signal representative ofthe desired pressure as a function of time. The programming deviceincludes the programming disc 6 shown in more detail in FIG. 5, which isfixedly mounted for rotation by a motor 7 through a timing device T. Asseen in FIG. 5, the program disc 6 is adapted to rotate about an axis ofmounting O. A lever 9 pivotally secured at point 0 and having a free end36 engages the edge portions of the disc 6, and when the disc rotatesthe lever sweeps a varying area which is a function of the instantaneousdistance of the free end 36 of lever 9 from the origin 0 of the programdisc 6. That is, by drawing an infinite number of radii from origin 0 ofthe disc to different portions of arc a-b, and taking the radius atpoint a as having a value of zero, it is seen that the radii increasesas the free end 36 of the lever 9 moves toward the point b. The free endof lever 9 then describes the pressure curve portion a-b which is seenin FIG. 6 and lasting during the time interval t By following the freeend 36 of the lever 9 from the point b to c on the program disc, it isseen that the radii which could be drawn from the origin 0 of the discto any point of the arc b-c, are constant, therefore, the lever 9, thatis its free end 36, describes a curve corresponding to portion b-c inFIG. 6 and lasting during the time interval 1 The spacing of the freeend 36 of the lever arm 9 from point 0 to d produces the curve portionc-d in FIG. 6- lasting during the time interval t The lever arm 9 isconnected through an arm 35 to a wiper arm 32 which is adapted to slideon resistor 34 of bridge circuit 30 and develop a voltage e which isrepresentative of the pressure conditions desired and as shown in FIG.6. The invention provides that the program disc is interchangeable andany desired pressure condition can be programmed with the apparatus ofthe invention by mounting a different program disc onto the axis 0. Thecalibration of bridge circuit 30 is such that if the pressurerepresented by the voltage e is equal to the desired pressurerepresented by the voltage e then the bridge 30' is balanced and nooutput voltage is developed across its terminals 40, 41. However, if theinstantaneous pressure represented by the voltage 2 is larger or greaterthan the desired pressure represented by the voltage e then a differencevoltage is developed across terminals 40, 41 which then, through variousnetworks such as shown diagrammatically by blocks 3, 4 and 5, isconnected via an amplifier 43 to a servo-motor M which operates thesetting of valve MV. The servo-motor M is further mechanically coupledwith a corrective bridge leg 42 which produces a balance voltage 2 as afunction of position of the valve MV. This balance voltage e is fed backto the input stage 4 to compensate the difference voltage applied to theterminals 40 and 41. In accordance with the sign of the balance voltagee developed between terminals 40, 41, the servo-motor is driven toincrease opening of the valve MV or to restrict the flow of pressurizedfluid through pneumatic circuit P when driven in the opposite direction.

During operation of the control apparatus, a start switch MS is closedalong with a switch S which connects motor 7 of the programming means toenergizing power source V while timer T is energized through the closingof switch S concurrently and starts at t as seen in FIG. 6. Energizationof timer T closes auxiliary switch S The closing of starting switch MSconnects the energizing coil of a solenoid R to source V and by beingenergized, the solenoid R closes contact pair 50, 51 and contact pair5253, while at the same time opens contact pair 54, 55, whereupon thesolenoid of valve V is deenergized which closes valve V preventingexhaustion of pressure from vessel 1 through circuit P' and the solenoidof V is energized which opens the valve V Valve V is now fully openedand permits pressurized fluid to flow from the source (not shown)through pneumatic branch P. Upon energization of the solenoid V byclosing switch S the bypass valve V is closed whereby the flow ofpressurized fluid from the pneumatic source is controlled only by theabove-described behavior of the valve MV, since the valve V is now fullyopened, and the actuation of the timer at t immediately closed auxiliaryswitch S While the programming means goes through the time cycles shownin FIG. 6 with the valves being in the state as described in connectionwith FIG. 4, the ultimate control of the pressure in the vessel 1proceeds in accordance with the operation described in connection withFIG. 2. As the pressure indicator 10 attains a set pressure which isrepresented by the curve at point a, the contact S opens up whereuponthe bypass valve V opens and the timer is deenergized. Deenergization ofthe timer T opens up auxiliary contact S whereupon the solenoid Rbecomes deenergized and the solenoids of valve V and V are reverted inthe initial state, that is, the valve V opens and connects the vessel 1to the atmosphere and the valve V closes preventing pressurized fluidfrom entering vessel 1 from the source (not shown). The programming disc6 rotates further since its motor 7 is still energized due to the factthat the contact S does not open until the programming disc completes afull revolution and returns to its original state, whereupon S opens anddeenergizes the motor 7.

It is seen that the apparatus in accordance with the invention providesreliable automatic control of the pressure in the vessel and maintainsit in accordance with a predetermined pressure program.

What is claimed is:

1. An apparatus for automatically controlling the fluid pressure in avessel according to a predetermined program, comprising a pressureconduit circuit including a branch for connecting said vessel to apressure fluid source; valve means provided in said conduit branch tocontrol fluid supply to said vessel; means for sensing the pressure insaid vessel and producing a first analogue signal in response thereto;programming means having a rotatable disc, the periphery of which isprofiled according to the desired pressure function; means forcontrolling the time of rotation of said profiled disc, follower levermeans engaging said profiled periphery and adapted for deriving a secondanalogue signal representing said predetermined pressure as a functionof time; comparison means adapted to compare said first and secondsignals and to produce a ditferential signal therefrom; valve controlmeans provided between said comparison means and said valve means tocontrol the latter in response to the sense and magnitude of saiddifferential signal; and balancing means adapted to produce a thirdsignal analogue to the position of said valve means, said third signalbeing fed back to said valve control means to compensate saiddiiferential signal.

2. Apparatus as claimed in claim 1, wherein said comparison meanscomprises at least a pair of resistor means connected into a balancedcircuit, varying means associated with each of said pair of resistors toshunt variably a portion of said resistor, the varying means of one ofsaid resistor means being coupled to said lever means to move inproportion therewith.

3. Apparatus as claimed in claim 2, wherein said pressure sensing meansincludes a transducer means producing an output representative of saidpressure variations, means responsive to the output of said transducermeans, the last-mentioned responsive means being coupled to the varyingmeans of the other of said pair of resistors for imparting a movement tosaid varying means proportional to the pressure variations in saidvessel.

4. Apparatus as claimed in claim 3, wherein the lastrnentionedresponsive means includes a phase sensitive bridge circuit having anoutput the phase of which varies in its sign in accordance with thevariation of the pressure in said vessel.

5. Apparatus as claimed in claim 4, wherein the lastmentioned responsivemeans further includes a servomotor coupled to the output of said phasesensitive bridge circuit.

6. Apparatus as claimed in claim 5, wherein said transducer means is adifferential transformer having a core movable in accordance with thepressure variations in said vessel.

7. Apparatus as claimed in claim 6, wherein said conduit circuitincludes another branch, second valve means disposed in said anotherbranch for connecting said vessel to the atmosphere when activated.

8. Apparatus as claimed in claim 7, wherein said disc means hasassociated therewith switch means, means for 10 driving said disc meansin cooperation with a timing means, said disc means effectingdisconnection of said switch means upon a complete revolution thereof,said switch means disconnecting the driving means upon said completerevolution.

9. Apparatus as claimed in claim 8, wherein said second valve means hasassociated therewith solenoid means disposed in an energizing circuit ofthe driving means, said solenoid means opening said second valve meansupon said complete revolution.

10. Apparatus as claimed in claim 9, including further valve meansdisposed in said one branch of said pneumatic circuit upstream of saidvalve means for permitting full flow of fluid thereto when actuated uponenergization of the driving means.

11. Apparatus as claimed in claim 10, wherein said solenoid meanscomprises a common actuating member for said second valve means and saidfurther valve means.

References Cited UNITED STATES PATENTS 602,548 4/1898 Williams et a1.137-50514 1,301,405 4/1919 Dexter 137505.14 2,661,577 12/1953 Hanson137505.17 2,818,081 12/1957 Eichenaver 137624.11 XR 2,984,251 5/1961Quinby 137-505.14 XR 3,017,556 1/1962 Smoot 137487.5 XR 3,180,356 4/1965Galley 137505.14 3,348,032 10/1967 Clardy et a1. 137624.11 XR M. CARYNELSON, Primary Examiner.

20 ROBERT J. MILLER, Assistant Examiner.

US. Cl. X:R.

